Device and method for monitoring a tank ventilation system

ABSTRACT

The invention relates to a device and a method for testing a tank ventilation system with a tank ventilation valve in a motor vehicle, comprising an engine speed sensor, an air flow sensor and/or an idle controller for providing an air mass signal, as well as an evaluating unit, which compares the changes in speed and air masses with at least one threshold value when the tank ventilation valve is opened and closed.  
     To improve the diagnosis of the tank ventilation system, it is proposed that the evaluating unit be designed in such a manner that a total reaction value, which is compared with a threshold value, is formed from the engine speeds when the tank ventilation valve is opened and closed as well as the air masses when the tank ventilation valve is closed and opened.

[0001] The invention relates to a device and a method for testing a tankventilation system according to the preamble of claim 1 or 4.

[0002] It is known to open and close selectively the tank ventilationvalve of a tank ventilation system for testing its operatability. Themotor reactions to the opening and closing of the tank ventilation valveare then examined. For example, if the speed and the air mass changewhen opening and closing the tank ventilation valve. In past systems,however, it is only known to compare each operating datum by itself witha threshold value in order to test altogether the operatability of thetank ventilation system.

[0003] Depending on how fast an idle controller reacts, however, to thechanges made by opening and closing the tank ventilation valve, theresults are different reactions. In the case of a slow idle controllerthe result will be predominantly a reaction in the speed. In the case ofa fast idle controller, the result will be predominantly a reaction inthe air mass. Moreover, all reactions in between, where both the speedand the measured and preset air mass change, are also, of course,possible. In total this means that the respective reaction is highlydependent on the application. In the event that the speed and the airmass change simultaneously, the amplitudes of each individual signal canvary widely. This state leads altogether to a poor signal to noiseratio.

[0004] The object of the present invention is to provide a device and amethod for testing a tank ventilation system. Said device and/or methodallows an accurate and flawless test of its operatability independent ofthe applications of an idle controller.

[0005] This problem is solved by the features disclosed in claim 1 or bythe features disclosed in claim 4.

[0006] The core idea of the present invention lies in the fact that eachrespective individual variable (operating datum) is not compared byitself with its own threshold value. Rather the different changes of theindividual variables are combined into a total reaction, which is thenevaluated. In the evaluation one can apply then the well-known method ofcomparison with a threshold value.

[0007] In the case of the inventive device and/or the inventive methodone proceeds from the hypothesis that in the case of an idling enginethe respective air masses and speeds are approximately proportional(n˜ml). One assumes in particular that, when the tank ventilation valveis closed, the quotient resulting from the air mass and speed isapproximately constant (ml₀:n₀=approximately constant).

[0008] Usually the air mass, which is additionally supplied by way ofthe tank ventilation valve, is not measured or specified. Therefore,when the tank ventilation valve is opened, more air is made available tothe engine than is preset by way of the idle controller. Thus, the totalair mass with the tank ventilation valve open is derived from themeasured air mass (ml) and the air mass ml_(TEV), flowing inadditionally by way of the tank ventilation valve.

[0009] In place of an air mass (ml), measured with an air flow sensor,the preset air mass nominal value (ml_nominal) of the idle controllercan also be used as the air mass signal. This feature is especiallyadvantageous if the measured air mass value cannot be resolved finelyenough or varies too much. Naturally the use of the air mass nominalvalue is also suitable as the air mass signal precisely when there is noair flow sensor.

[0010] In an advantageous embodiment a relative change in the air massis computed from the air mass and the engine speed when the tankventilation valve is opened and from the air mass and the speed when thetank ventilation valve is closed. The relative air mass can becalculated, on the one hand, from a difference of the quotient resultingfrom the speed for an opened tank ventilation valve and the speed for aclosed tank ventilation valve, as well as, on the other hand, from thequotient resulting from the air mass with the tank ventilation valveopen and the air mass with the tank ventilation valve closed.

[0011] The methods disclosed in the patent claims are suitable foroperating the device, according to the invention.

[0012] The present invention is explained in detail below by means of anembodiment and with reference to the attached drawings.

[0013]FIG. 1 is a schematic block diagram of an embodiment of thepresent invention; and

[0014]FIG. 2 depicts a simple method for operating the device, accordingto FIG. 1.

[0015]FIG. 1 is a schematic block diagram of an engine 1 with an exhaustchannel 5 and an intake area 3. In the intake area 3 a throttle valve 2and an air flow sensor 12 are connected in series. The air flow sensor12 measures the air mass moving through an intake channel and sends acorresponding signal to an evaluating unit 14.

[0016] In addition, the engine 1 exhibits a speed sensor 10, which alsosends its speed signal to the evaluating unit 14. Furthermore, athreshold value 16 is stored in the evaluating unit 14.

[0017] The throttle valve 2 is actuated, among other things, by an idlecontroller 13, which sends an air mass nominal value ml_nominal, whichis equivalent to the degree that the throttle valve is open, to theevaluating unit 14.

[0018] Furthermore, there is a tank ventilation system, of which in thepresent drawing only the tank ventilation valve 7 with a feed channel 8is shown. The air, flowing through the tank ventilation valve 7, is fedto the intake area 3 by way of the feed channel 8. The tank ventilationvalve 7 can be closed or opened (see actuation shown by the arrow).

[0019] Depending on the switching state of the tank ventilation valve 7there is an engine reaction in the form of a change in the engine speedand/or the air mass, flowing through the intake area 3.

[0020] At this stage in the present embodiment the tank ventilationsystem is tested in such a manner that first the air mass ml₀ and therelated speed n₀ are measured with the tank ventilation valve 7 closed(step 50 in FIG. 2).

[0021] Then the tank ventilation valve 7 is opened (step 52).

[0022] Subsequently the air mass ml and the related speed n are measuredwith the tank ventilation valve 7 open (step 54).

[0023] Then a total reaction value is calculated in step 56. In thepresent embodiment one assumes that, when the engine is idling, the airmass and the speed are approximately proportional (n˜ml). The result isthat the quotient derived from the air mass and the speed isapproximately constant:

ml ₀ /n ₀ is approximately constant.

[0024] In contrast, when the tank ventilation valve 7 is opened, theresult is a total air mass ml+nl_(TEV), where ml_(TEV) describes the airflow through the tank ventilation valve 7.

[0025] Thus, the result is altogether the equation:

ml ₀ /n ₀=(ml+ml _(TEV))/n

[0026] Following transformation, the result is:

ml _(TEV) /ml ₀ =n/n ₀ −ml/ml ₀

[0027] Thus, the quotient resulting from ml_(TEV)/ml₀ characterizes therelative change in the air mass. In the present case it is also thetotal reaction value, which describes altogether the engine reaction.

[0028] The tank ventilation valve 7 is opened in an advantageous mannercontinuously, that is ramp-like or step-like. At the same time the steps54, 56 and 58 are carried out. If one reaches the threshold value instep 58, the tank ventilation valve 7 does not have to be opened anyfurther.

[0029] Of course, one can also carry out analogously the reactionevaluation from an opened tank ventilation valve to a closed tankventilation valve. In carrying out the process in both directions oneobtains maximum information from the selective opening or closing of thetank ventilation valve and thus concomitant certainty of diagnosis.

[0030] Then the total reaction value, thus in the present case therelative change in the air mass, is compared with the threshold value16; and depending on whether the value exceeds or falls below thethreshold value, one obtains information on whether the tank ventilationvalve 7 and the tank ventilation system are functioning altogetherflawlessly.

[0031] If the air mass signal, coming from the air flow sensor 12,fluctuates too much, one can resort to the air mass nominal valueml_nominal, which comes from the idle controller 13 and which is used asa substitute for the air mass value ml, to be measured.

[0032] With the present invention one is relatively independent of anapplication of the idle controller. Furthermore, one achieves a bettersignal to noise ratio than with the method described in the introductorypart of the specification. Moreover, the tank ventilation valve does nothave to be opened far until a specific reaction occurs. Thus, this meansless interruption in the idle position during a test run. Moreover, thedesign of the present method is simpler than the originally appliedmethod, since only one variable, namely the total reaction, must beapplied.

Device and method for testing a tank ventilation system patent claims:1. Device for testing a tank ventilation system with a tank ventilationvalve in a motor vehicle, comprising an engine speed sensor (10), an airflow sensor (12) and/or an idle controller (13) for providing an airmass signal, as well as an evaluating unit (14), which compares thechanges in speed and air masses with at least one threshold value whenthe tank ventilation valve is opened and closed, characterized in thatthe evaluating unit (14) is designed in such a manner to form a totalreaction value from the engine speeds and the air masses when the tankventilation system is opened and closed and to compare this value with athreshold value.
 2. Device, as claimed in claim 1, characterized in thata relative change in the air mass (ml_(TEV)/ml₀) can be calculated fromthe air mass and the engine speed when the tank ventilation valve (ml,n) is opened, and from the air mass and the speed when the tankventilation valve is closed (ml₀/n₀).
 3. Device, as claimed in claim 2,characterized in that the relative air mass (ml_(TEV)/ml₀) iscalculated, on the one hand, as the difference of the quotients from thespeed when the tank ventilation valve (n) is opened and the speed whenthe tank ventilation valve (n₀) is closed, and, on the other hand, theair mass when the tank ventilation valve (ml) is opened and the air masswhen the tank ventilation valve (ml₀) is closed.
 4. Method for testing atank ventilation system with the steps measuring the engine speed whenthe tank ventilation valve is closed (n₀), measuring the engine speedwhen the tank ventilation valve is opened (n), measuring or determiningan air mass when the tank ventilation valve is closed (ml₀), measuringor determining an air mass when the tank ventilation valve is opened(ml), forming a total reaction value from the measured speeds and themeasured or determined air masses and comparing the total reaction valuewith the preset threshold value.
 5. Method, as claimed in claim 4,characterized in that a relative change in the air mass (ml_(TEV)/ml₀)is calculated from the air mass and the speed when the tank ventilationvalve is opened and from the air mass and the speed when the tankventilation valve is closed.
 6. Method, as claimed in claim 5,characterized in that the relative air mass is calculated, on the onehand, as the difference of the quotients from the speed when the tankventilation valve (n) is opened and the speed when the tank ventilationvalve (n₀) is closed, and, on the other hand, the air mass when the tankventilation valve (ml) is opened and the air mass when the tankventilation valve (ml₀) is closed.